CMSIS-Core (Cortex-M)  Version 5.6.0
CMSIS-Core support for Cortex-M processor-based devices
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Startup File startup_<device>.c

The Startup File startup_<device>.c contains:

  • The reset handler which is executed after CPU reset and typically calls the SystemInit function.
  • The setup values for the Main Stack Pointer (MSP).
  • Exception vectors of the Cortex-M Processor with weak functions that implement default routines.
  • Interrupt vectors that are device specific with weak functions that implement default routines.

The file exists for each supported toolchain and is the only tool-chain specific CMSIS file.

To adapt the file to a new device only the interrupt vector table needs to be extended with the device-specific interrupt handlers. The naming convention for the interrupt handler names are <interrupt_name>_IRQHandler. This table needs to be consistent with IRQn_Type that defines all the IRQ numbers for each interrupt.

Example:

The following example shows the extension of the interrupt vector table for the LPC1100 device family.

/*----------------------------------------------------------------------------
Exception / Interrupt Handler
*----------------------------------------------------------------------------*/
/* Exceptions */
void WAKEUP0_IRQHandler (void) __attribute__ ((weak, alias("Default_Handler")));
void WAKEUP1_IRQHandler (void) __attribute__ ((weak, alias("Default_Handler")));
void WAKEUP2_IRQHandler (void) __attribute__ ((weak, alias("Default_Handler")));
// :
// :
void EINT1_IRQHandler (void) __attribute__ ((weak, alias("Default_Handler")));
void EINT2_IRQHandler (void) __attribute__ ((weak, alias("Default_Handler")));
// :
// :
/*----------------------------------------------------------------------------
Exception / Interrupt Vector table
*----------------------------------------------------------------------------*/
extern const pFunc __VECTOR_TABLE[240];
const pFunc __VECTOR_TABLE[240] __VECTOR_TABLE_ATTRIBUTE = {
(pFunc)(&__INITIAL_SP), /* Initial Stack Pointer */
Reset_Handler, /* Reset Handler */
NMI_Handler, /* -14 NMI Handler */
HardFault_Handler, /* -13 Hard Fault Handler */
MemManage_Handler, /* -12 MPU Fault Handler */
BusFault_Handler, /* -11 Bus Fault Handler */
UsageFault_Handler, /* -10 Usage Fault Handler */
0, /* Reserved */
0, /* Reserved */
0, /* Reserved */
0, /* Reserved */
SVC_Handler, /* -5 SVC Handler */
DebugMon_Handler, /* -4 Debug Monitor Handler */
0, /* Reserved */
PendSV_Handler, /* -2 PendSV Handler */
SysTick_Handler, /* -1 SysTick Handler */
/* Interrupts */
WAKEUP0_IRQHandler, /* 0 Wakeup PIO0.0 */
WAKEUP1_IRQHandler, /* 1 Wakeup PIO0.1 */
WAKEUP2_IRQHandler, /* 2 Wakeup PIO0.2 */
// :
// :
EINT1_IRQHandler, /* 30 PIO INT1 */
EINT2_IRQHandler, /* 31 PIO INT2 */
// :
// :
};

startup_Device.c Template File

A compiler agnostic startup_Device.c Template File for an Armv7-M processor like Cortex-M3 is shown below. The C startup file relys on certain compiler specific preprocessor defines specified in CMSIS compiler headers:

/******************************************************************************
 * @file     startup_<Device>.c
 * @brief    CMSIS-Core(M) Device Startup File for
 *           Device <Device>
 * @version  V1.0.0
 * @date     20. January 2021
 ******************************************************************************/
/*
 * Copyright (c) 2009-2021 Arm Limited. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "<Device>.h"

/*---------------------------------------------------------------------------
  External References
 *---------------------------------------------------------------------------*/
extern uint32_t __INITIAL_SP;
extern uint32_t __STACK_LIMIT;
#if defined (__ARM_FEATURE_CMSE) && (__ARM_FEATURE_CMSE == 3U)
extern uint32_t __STACK_SEAL;
#endif

extern __NO_RETURN void __PROGRAM_START(void);

/*---------------------------------------------------------------------------
  Internal References
 *---------------------------------------------------------------------------*/
__NO_RETURN void Reset_Handler  (void);
__NO_RETURN void Default_Handler(void);

/* ToDo: Add Cortex exception handler according the used Cortex-Core */
/*---------------------------------------------------------------------------
  Exception / Interrupt Handler
 *---------------------------------------------------------------------------*/
/* Exceptions */
void NMI_Handler            (void) __attribute__ ((weak, alias("Default_Handler")));
void HardFault_Handler      (void) __attribute__ ((weak));
void MemManage_Handler      (void) __attribute__ ((weak, alias("Default_Handler")));
void BusFault_Handler       (void) __attribute__ ((weak, alias("Default_Handler")));
void UsageFault_Handler     (void) __attribute__ ((weak, alias("Default_Handler")));
void SecureFault_Handler    (void) __attribute__ ((weak, alias("Default_Handler")));
void SVC_Handler            (void) __attribute__ ((weak, alias("Default_Handler")));
void DebugMon_Handler       (void) __attribute__ ((weak, alias("Default_Handler")));
void PendSV_Handler         (void) __attribute__ ((weak, alias("Default_Handler")));
void SysTick_Handler        (void) __attribute__ ((weak, alias("Default_Handler")));

/* ToDo: Add your device specific interrupt handler */
void <DeviceInterrupt first>_Handler     (void) __attribute__ ((weak, alias("Default_Handler")));
...
void <DeviceInterrupt last>_Handler      (void) __attribute__ ((weak, alias("Default_Handler")));


/*----------------------------------------------------------------------------
  Exception / Interrupt Vector table
 *----------------------------------------------------------------------------*/

#if defined ( __GNUC__ )
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"
#endif

/* ToDo: Add Cortex exception vectors according the used Cortex-Core */
extern const VECTOR_TABLE_Type __VECTOR_TABLE[<Device vector table entries>];
       const VECTOR_TABLE_Type __VECTOR_TABLE[<Device vector table entries>] __VECTOR_TABLE_ATTRIBUTE = {
  (VECTOR_TABLE_Type)(&__INITIAL_SP),  /*     Initial Stack Pointer */
  Reset_Handler,                       /*     Reset Handler */
  NMI_Handler,                         /* -14 NMI Handler */
  HardFault_Handler,                   /* -13 Hard Fault Handler */
  MemManage_Handler,                   /* -12 MPU Fault Handler */
  BusFault_Handler,                    /* -11 Bus Fault Handler */
  UsageFault_Handler,                  /* -10 Usage Fault Handler */
  SecureFault_Handler,                 /*  -9 Secure Fault Handler */
  0,                                   /*     Reserved */
  0,                                   /*     Reserved */
  0,                                   /*     Reserved */
  SVC_Handler,                         /*  -5 SVCall Handler */
  DebugMon_Handler,                    /*  -4 Debug Monitor Handler */
  0,                                   /*     Reserved */
  PendSV_Handler,                      /*  -2 PendSV Handler */
  SysTick_Handler,                     /*  -1 SysTick Handler */

/* ToDo: Add your device specific interrupt vectors */
  /* Interrupts */
  <DeviceInterrupt first>_Handler,     /* first Device Interrupt */
  ...
  <DeviceInterrupt last>_Handler       /* last Device Interrupt */
};

#if defined ( __GNUC__ )
#pragma GCC diagnostic pop
#endif

/*---------------------------------------------------------------------------
  Reset Handler called on controller reset
 *---------------------------------------------------------------------------*/
__NO_RETURN void Reset_Handler(void)
{
  __set_PSP((uint32_t)(&__INITIAL_SP));

/* ToDo: Initialize stack limit register for Armv8-M Main Extension based processors*/
  __set_MSPLIM((uint32_t)(&__STACK_LIMIT));
  __set_PSPLIM((uint32_t)(&__STACK_LIMIT));

/* ToDo: Add stack sealing for Armv8-M based processors */
#if defined (__ARM_FEATURE_CMSE) && (__ARM_FEATURE_CMSE == 3U)
  __TZ_set_STACKSEAL_S((uint32_t *)(&__STACK_SEAL));
#endif

  SystemInit();                    /* CMSIS System Initialization */
  __PROGRAM_START();               /* Enter PreMain (C library entry point) */
}


#if defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050)
  #pragma clang diagnostic push
  #pragma clang diagnostic ignored "-Wmissing-noreturn"
#endif

/*---------------------------------------------------------------------------
  Hard Fault Handler
 *---------------------------------------------------------------------------*/
void HardFault_Handler(void)
{
  while(1);
}

/*---------------------------------------------------------------------------
  Default Handler for Exceptions / Interrupts
 *---------------------------------------------------------------------------*/
void Default_Handler(void)
{
  while(1);
}

#if defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050)
  #pragma clang diagnostic pop
#endif

startup_Device.c Template File (Armv8-M/v8.1-M)

The C-startup file for an Armv8-M/v8.1-M processor is similar to the one for an Armv7-M processor except that it offers the possibility of stack sealing for the Main Stack Pointer (MSP). The following preprocessor defines and CMSIS functions are used:

The stack sealing and the initialization fof the Stack Limit register is done in function void Reset_Handler(void):

/*----------------------------------------------------------------------------
Reset Handler called on controller reset
*----------------------------------------------------------------------------*/
__NO_RETURN void Reset_Handler(void)
{
__set_PSP((uint32_t)(&__INITIAL_SP));
__set_MSPLIM((uint32_t)(&__STACK_LIMIT));
__set_PSPLIM((uint32_t)(&__STACK_LIMIT));
#if defined (__ARM_FEATURE_CMSE) && (__ARM_FEATURE_CMSE == 3U)
#endif
SystemInit(); /* CMSIS System Initialization */
__PROGRAM_START(); /* Enter PreMain (C library entry point) */
}
Note
Stack Sealing also requires the application project to use a scatter file (or a linker script) as explained in Stack Sealing section.